As shown in FIG. 1, a switching node generally consists of peripheral units (connection equipment for subscribers or lines), a central computer platform, message distribution equipment, and other, central units such as a switching network, protocol termination equipment (for Signaling System No. 7, for example), a background memory, and operating equipment etc.
The peripheral equipment performs essential call-processing functions associated with the voice channels of the peripheral equipment. Said equipment therefore contains call-processing and administration & maintenance programs and the data information associated with the equipment such as port assignment, signaling, classes-of-service, directory numbers, individual characteristics of trunk circuits and subscriber lines, and the capacity level and configuration of the peripheral equipment.
The central computer platform coordinates and controls the connection setup and cleardown process and the responses to administrative configuration changes and to such changes due to faults.
The classical peripheral equipment terminates the trunk circuits for whose handling in call-processing terms it is responsible. The various items of peripheral equipment are linked via the message distribution system to each other and to the common computer platform. The other central system components make special functions, for example for through-connecting the voice channels, processing the signaling protocols, implementing the operator interface, or storing bulk data, available to the switching system.
For fault-tolerance reasons the central components of a switching system are of redundant design (duplicated, for example). The peripheral equipment is generally not of redundant design. It can, however, be of redundant design when fault-tolerance requirements are more stringent (maintaining stable connections when an item of peripheral equipment fails, for instance).
Limitations as regards the number of voice channels that can be terminated no longer apply when signaling and voice transmission take place in a dissociated manner on separate paths and the peripheral equipment's only function is signal processing and/or conversion with no physical termination of the voice channels. For this application, said logical peripheral equipment is determined in terms of its capacity by the power of the processors, the size of the memory, and the capacity of the message interface.
Since more than one route has to be made available for through-connecting voice between an A-subscriber or an A-side trunk (which is to say a trunk circuit to a far-end switching center) and any B-subscriber or a B-side trunk, two different items of peripheral equipment (PE) are generally involved in the connection setup and cleardown process, as is shown in FIG. 2.
The switching center responsible for controlling connections routed outside the switching center can make subscriber or network features known from classical telephone networks (such as TDM networks—TDM: Time Division Multiple Access) available to the A- and/or B-side subscriber. Said features include, in particular, announcements and dialogs which are necessary in certain situations (such as “The number you have dialed is unobtainable”, “The number you have dialed has changed; the new number is 722-25940.” or determining the class-of-service for dialing into a packet network).
In the classical case where the connection's useful channel is routed into the switching center, these announcements and dialogs can be provided by peripheral equipment having suitable functionality. If, however, the useful data is routed outside the switching center in a packet network, an external system is preferably employed for this. Said external system has interfaces to the packet network for the useful data consisting of announcements and user entries. The external announcement and dialog system (also: IVR system or Interactive Voice Response system) furthermore has a logical control interface to the switching center responsible in the packet network for controlling connections routed outside the switching center, as is shown in FIG. 2.
In the prior art, available IVR systems are generally TDM-based (TDM: Time Division Multiplex) and combine the entire range of functions in order to be universally applicable. This universality has the disadvantage of cost, requiring that maximum effective use be made of an IVR system. Two application scenarios are customary in TDM-based data transmission networks with conventional switching centers (the classical telephone network, for example), as described below:
On the one hand, peripheral equipment of the switching center with hardware modules for providing announcements and DTMF (Discrete Tone Multi-Frequency) signal recognition and/or voice recognition is introduced into the switching center. To play an announcement or dialog, the subscriber/trunk is switched via a 64-kbit/s through-connection to a port of the special peripheral equipment for announcements and dialogs. From the call-processing viewpoint this is a through-connection from an item of A-side peripheral equipment via the switching network to the B-side peripheral equipment with announcement and dialog functionality. The B-side announcement/dialog port acts like a B-side trunk. The type of announcement to be played or type of dialog functions is indicated by means of signaling within the switching center to the peripheral equipment with announcement and dialog functionality, or is permanently pre-defined.
The advantage of this implementation lies in the announcement and dialog functionality's being integrated in the switching center, which is very economical in terms of cost. Broad access to the hardware functionality of the peripheral equipment for announcement and dialog functionality is also facilitated.
The disadvantage of this implementation arises from the fact that if the useful channel is routed on a packet basis or outside the switching center, this functionality cannot be used or can only be used with an upstream gateway (see also FIG. 3) serving as the network interworking point between the TDM-based data transmission network (classical telephone network) and packet network (such as the internet). Furthermore, the voice data which in the prior art is presented in PCM/TDM (Pulse Code Modulation/Time Division Multiplex) technology must be converted into packet data. A load in terms of useful data for announcements and dialogs furthermore arises in the controlling switching center and there is a loss of speech quality due to conversion of the useful data from the TDM/PCM system into packet data.
On the other hand, announcements and dialogs are also made available at the network interworking point between the packet and TDM network as well, or by packet-based IVR systems specially designed for announcement and dialog functions. The announcement and dialog functions are here controlled by the switching center's call control server controlling the connection.
The advantages of this system lie in its being able to be used in packet networks without the need to provide TDM equipment for it, there being no need for additional conversion of the useful data from the TDM system into packet data. However, the disadvantage of this system arises from the fact that the switching center controlling the switching center for connections routed in the packet network cannot access the IVR functions in the packet network.